In a large number of mobile storage systems, mobile storage units are selectively movable with respect to one another in some manner, such as along tracks or rails to which the units are mounted. The units can be moved along the tracks or rails in a manually operated manner, or through the use of a motor operably connected to wheels disposed on the storage unit and rotatably engaged with the rails to enable the storage unit to move with respect to the rails. In those storage units employing an electric motor, upon activation of the motor by a user activated switch, the motor operates a drive system that rotates the wheels of the unit to move the unit along the rails in the desired direction.
Most prior art motorized mobile storage systems utilize one of two basic modes of operation. The first is a “push and hold” mode of operation. In a push and hold system, an operator “manually” moves one carriage at a time by pressing and holding a move button on a mobile storage unit until the unit reaches a desired location and the button is released. The main problem with such a system is that if several mobile storage units need to be moved in order open a desired aisle, the operation can be time consuming in that a user must sequentially move multiple aisles. Despite its shortcomings, the push and hold method of operation does provide benefits in that it provides an operator full control of the system. The operator can look down the aisle as the aisle is closing to ensure that the aisle is clear. If there is an obstruction in the aisle, the operator can stop the system by releasing the move button. The operator can further manually set the aisle width to accommodate for large overhanging objects or other obstructions that may protrude from the storage units into an aisle.
An alternative to the push and hold system is the “automatic” or “one touch move” system. In this type of system, an operator presses a button selecting the aisle or 4mobile storage unit to move, and the selected aisle opens by movement of the appropriate mobile storage unit. The mobile storage units move until a limit switch or other device is triggered, which occurs when the mobile storage unit has reached its end position. This end position (the distance between adjacent units) is typically adjustable only by a service technician. Such adjustment requires the technician to either physically adjust the position of a mechanical limit switch or set a new limit via software. While the automatic mode of operation is less time consuming than the push and hold mode of operation, the automatic mode does not allow the operator to control movement of the storage units when forming an aisle. Instead, mobile storage systems of this type incorporate a passive safety system to detect the presence of objects or obstructions between storage units, and the drive arrangement of each storage unit is responsive to the passive safety system to stop movement of the storage unit if an object is detected as an aisle is being closed. However, many known safety systems do not adequately detect overhanging shelved objects. If such objects protrude past the limit switch, it is possible that such objects may be struck by a moving carriage before the limit switch is reached and movement of the storage unit it stopped.
Therefore, it is desirable to develop a mobile storage system that combines the speed and efficiency of an automatic mode of operation with the user control provided by push and hold systems. Such a system would preferably allow a user to select an aisle and then manually move several carriages at a time as the selected aisle is opened. It is also desirable to develop a mobile storage system having the advantages discussed above, and which is further capable of maintaining the aisle width established by an operator in a move operation in subsequent operations to thereby protect overhanging media or other objects located in an aisle.